CH temper mental

[Mr. Tickle]

Felix,

If the dial is cubic foot, I am using 0.1 cubic feet per minute, not 1ft3.

Is that right?

Thanks again.

Do you think I should call someone and give them this info? Can anyone recommend anybody who might be able to solve this problem for me? It's getting colder and colder.

Mr. Tickle.

 

[ChrisR]

You mean it moves just one sector/division in a minute? That's not enough to do more than worm the rads a little, assuming the heat is spread throughout.
It could be that the gas valve sticks when it's hot and doesn't open much.

I would think what we'd all do, having checked the voltages on the gas valve and the pressure it's giving out (which you can't quite so easily, though you can get someone watching the meter), would be to tap the gas valve with the handle of a small screwdriver. Someone will probably now accuse me of telling you to belt it with a sledge hammer.
It won't do any harm if you can get at it easily without taking the combustion chamber cover off. Be Careful it has mains voltages on it.

If there's the slightest sign that the flames alter or the gas rate changes, get a new gas valve put in by a corgi.

 

[Mr. Tickle]

The gas valve being under the boiler? The small blue thing?

I can take the bottom bit off without getting into the combustion chamber and it has the dial to turn up the boiler. I should give that a tap?

Or are you talking about the valve outside?

Yes, it moves one segment. I was watching it last night when the rads were really hot.

I am going to look through to the pilot light - I'm not sure I can see the actual burners. I have to say that i can hear a whoosh when it clicks on, which sounds like gas being ignited. But if i do tap the valve and it makes a difference -should i be able to see something happening through the little 8mm viewing hole?

Thanks again!

Mr. Tickle.

 

[ChrisR]

Glowworm gas valves often had blue round "hat" shaped knobs on their gas valves. GV itself is a grey aluminium alloy casting, 2-3 inches square by 5 ish inches long. So it sounds right. Tap the body of the thing. You might see the flames alter but with an 8mm hole they don't make it easy. There might be an orange moment when you whack - sorry - tap, it.
You could also try pushing the blue knob in, if it moves - can't remember what it does inside but it might exercise something.

WHat you should be able to see, once the boiler is hot, is the effect of turning the knob - ie the temperature thermostat. There will be a LOT of hysteresis (free play, in effect) but if you turn the knob high when the flames are out they should light up, and V-V. They go right out once the boiler thinks it's hotter than the knob setting.

 

[Mr. Tickle]

There is a seperate dial that controls the gas - and then there's a blue valve - is that right?

I'm really sorry to troll on about little things, but I must make sure I have this right.

You're saying that if I bang/tap the valve, if there's something stuck it will unstick a bit, letting gas through. I should be able to see this as it burns off inside the chamber.

I am not aware that there is a time when the gas is 'out' but the boiler is on - so i'm not going to be able to turn it up when it's out and see it fire.

When we first moved in - we noticed a smell of gas along the street. There's a gas building at the end of our road, nearly next door to us. One of those 'MEB' sheds.

I could only smell it occasionally at around 5/6 pm. I called and BG came out to test it. I spoke to the engineer who said that as the main gas line branches off to the smaller house feeds, any excess is vented to the atmosphere.

He said this usually happens around the time of day when everyone is coming in from work, turning everything on and the usage goes up.

Is this right, or could the smell of gas be coming out the flue/vent at the front of the house?

I'm really really lost. I've spoken to another heating engineer today who has no idea what I'm talking about and seemed to think i was messing him about. Everyone wants to replace the pump and valve and won't believe that the two pipes coming from the boiler are cold.

Again, I apologise for this continued thread. Your help really is appreciated. If this is resolved, i'll be mailing beer out to all the useful responders!

Mr. Tickle.

 

[ChrisR]

Dis is a gas valve, though they vary:

I didn't mean this sort of thing

YOu might not notice the flames increase through an 8mm hole so time gas use at meter.

 

[Mr. Tickle]

Okay, this is great!

I have looked at the flame - when i hit it, i can see that it changes and I do see a 'gust' of orange flame when it flickers. The flame that i can see is jumping around a bit, not exactly stable like on the cooker hob.

I have also been monitoring the whole system and writing down all the times and positions/reading of everything as it works and doesn't work.

I can't figure out why just yet - but the gas being used changes from a noticable-meter-needle-moving-quickly 0.5ft3/min to a slow-jerky 0.18/0.2 ft3/min.

I am going to buy a multimeter this afternoon so I can check the voltages on the 3way valve. If this shows that the voltage is too low - I need to call someone in to service the gas valve or is the gas valve fine, only it's not getting the voltage V-V it's the 3way that needs replacing?

Thanks again.

Mr. Tickle

 

[felix]

You're right to check the voltage before you change what might be a perfectly good gas valve. When you demand HW only on a normal three port system, power for the gas valve comes from the controller through the tank stat. When you demand CH as well this drives the valve to mid position but the HW demand still powers the gas valve. It's only when you demand CH on its own that the gas valve gets power through the three port. From what you've described so far, you do NOT have a faulty three port valve.

 

[Mr. Tickle]

I see that, thank you Felix. But yes, i will check first to ensure it is getting the correct voltage.

I feel I am getting nearer to the problem! Which is nice.

I managed to get the boiler manual from Glow Worm without dialing 09 numbers. It says the minimum allowed gas flow rate is 25.8ft3/h.

At 0.2ft3/min, that makes 12ft3/hr - half what it's supposed to be.

Can i presume that this is enough to get the pilot light going and keep the fan thingy going but not enough to do anything to the heat?

Cheers.

Mr. Tickle.

 

[felix]

Correct. Your boiler is running on simmer. This would be enough to heat your water cylinder, though it would take a long time, but your radiators will not do so well.

Your pilot light, if you can see it, is another clue to the source of the problem. If it shrinks away when the gas flow rate drops you should look for a partial blockage upstream. It might be that the gas supply in your area is simply not up to the job. Alternatively, do you have a joker in the house fiddling with the gas stop cock at the meter? If the pilot remains steady then the problem is in the valve or its volts.

 

[Mr. Tickle]

There isn't anyone fiddling with the gas mains, no. I can't imagine there would be someone coming to the front of the house everyday at a specific time and changing it!

How do I measure the valve voltage again?

I've unscrewed the fittings on the top of the valve (A Danfoss T45(?)) but the whole plastic thing lifts off the brass plate and there are no contacts there.

Should i be measuring the voltages inside the white connection box?

Will the Sw L be be marked and if so, what do a measure it against? Is there a Sw N that i can measure the voltage across?

Should it read 240v or there abouts? A continuous voltage or will it just throw 240v at it to open the valve?

I think we're getting close, people!

Cheers.

Mr. Tickle.

 

[felix]

I think you'll have to look at the point where outside wiring comes into your boiler. Is this what you mean by the connection box?

You should find at least three wires in there: switched live, neutral and earth, but there will probably be others too. Two common ones are permanent live (so watch your fingers) and a switched live OUT for the pump. There might also be multiple earth and neutral terminals but a close inspection (power OFF for this) will show that these are linked.

Identify the earth terminal(s) first. There should be no mistaking these because the wires are supposedly green/yellow. If one of them is visibly connected to the boiler's metalwork that clinches it.

Next you find the neutral(s). These should have black or blue wires in them. Confirm a neutral by measuring its voltage with respect to earth. There should be little or nothing there whether the boiler/pump are running on not.

You measure your switched live volts with respect to neutral, though you could use earth at a pinch. You'll have to establish which of the other wires is in fact the gas valve's switched live but that's not as hard as it sounds. A permanent live will be easy to identify and a pump live feed isn't too difficult either. The voltage on switched live comes and goes as the boiler goes on and off, but note that the boiler's own thermostat can turn the gas off even if switched live is present.

Do remember that you've got potentially dangerous voltages in there. Just about the worst thing you can do is to hold onto the boiler with one hand while prodding around live terminals with the other! I recommend clipping a meter lead onto neutral - or earth as a last resort - and making the measurements with your other hand in your pocket

 

[ChrisR]

Quite a little saga this one's turning into! Still, we'll get there. For people who ask about reiability of combis, I think we're about at the stage where the combi would be heading for the bin, or expensive part-swaps in the hope of hitting the problem. With this sort of problem where the thing's working but not enough to do the job, there could be a lot of bits to wonder about - sensors, modulating (variable) gas valves, settings on multiple switches on sometimes lazy diverters, pcbs...

One small complication this Glowie might have - is the Gas Valve a 24V one or mains? Careful inspection of the GV should find it writ somewhere - apart from finding a transformer.
And what about pump overrun? Did you find a model name/ number, Mr T?

 

[Mr. Tickle]

What I mean by connection box - there is this white flatish (what looks like to me as a) distribution box by the HW tank. THe wires for the Tank Therm and the valve to there - and there are wires leading off into the depths of my floorboards.

I was going to open that up and check the voltages.

I have looked under my boiler but I can't find many electircal connections that could be probed - i'd have to push through the wire sheath which i don't want to do.

If I've got to start poking around with the mains voltage leading into my house - surely that's another problem all together? I thought the idea about the voltage difference was that the switch in the valve wasn't sending the full voltage to the boiler.

How would it not send enough voltage?

Mr. Tickle.

 

[felix]

Although the supply to the gas valve can be found in that box, measuring it in there won't really tell you enough. If the problem really is electrical it's quite likely to be a bad connection at the boiler end. That would certainly explain why strange things happen when you hit it. It could also explain why everything works properly for a while then, when boiler heat reaches the bad joint, things go wrong.

You will only find out if it is a bad connection if you can gain access to the terminals in the boiler. Since you can see the cables at the boiler but not their terminations, you'll have to open up some kind of access panel to get any further. There WILL be a way to do this because somebody wired it up. Whether or not you WANT to do it is another matter. You should certainly turn the power off first.

PS: I don't blame you for not wanting to pierce the cable insulation. I wouldn't do it either. You'ld have to break through two layers and there's a distinct possibility of causing a short circuit. Bad plan!